Low bake, low voc conductive primer

Abstract

The present invention provides for a sealer/primer that is generally cured at low bake temperatures. The composition utilizes a resin system to provide both conductivity and adhesion of the coating onto plastic substrates. The present invention uses a polyester, such as one that includes unsaturated polyester, in combination with other resins, including an acrylic, crosslinking agent and conductive pigment to create a conductive primer that can be cured at low temperatures. The composition can be applied through traditional application equipment, seals the surface of the substrate to which it is applied, and cures to an acceptable surface for further processing, such as painting.

1 . A method of priming and sealing a plastic substrate, comprising
 spraying onto the substrate a coating composition comprising,
 (a) resin system, wherein said resin system includes at least one hydroxy functional unsaturated polyester and at least one hydroxy functional acrylic polymer; 
 (b) a crosslinker selected from the group consisting of amino resins and isocyanates; and 
 (c) a conductive pigment; 
 wherein said unsaturated polyester is unsaturated in the backbone of the polyester and does not undergo further crosslinking in the coating composition through its unsaturation. 
   
   
   
       2 . The method of  claim 1 , wherein said polyester contains about 5% to about 60% of unsaturated dibasic acids or anhydrides. 
   
   
       3 . The method of  claim 1 , wherein said polyester contains secondary hydroxyl functionality. 
   
   
       4 . The method of  claim 1 , wherein said polyester has a weight average molecular weight from about 700 to about 1300. 
   
   
       5 . The method of  claim 1 , wherein said polyester has an OH value from about 50 to about 400 mg KOH/g. 
   
   
       6 . The method of  claim 1 , wherein said acrylic has an OH value from about 20 to about 200 mg KOH/g. 
   
   
       7 . The method of  claim 1 , wherein said acrylic has a weight average molecular weight from about 1600 to about 7000. 
   
   
       8 . The method of  claim 1 , The composition of  claim 1 , wherein the unsaturated polyester comprises from about 10% to about 90% by weight of the resin system. 
   
   
       9 . The method of  claim 1 , wherein said crosslinker is an isocyanate. 
   
   
       10 . The method of  claim 9 , wherein the crosslinker is present in a ratio of about 0.8 to about 1.2 based on the NCO:OH ratio. 
   
   
       11 . The method of  claim 1 , wherein the substrate is selected from the group consisting of acrylonitrile butadiene styrene, polycarbonate-acrylonitrile butadiene styrene, polydicyclopentadiene, sheet molding compound, bulk molding compound, reaction injection molding, reaction thermal molding, polycarbonate, polyphenylene oxide, polycarbonate polyester, and hybrid molding. 
   
   
       12 . The method of  claim 1 , wherein said crosslinker is an amino resin. 
   
   
       13 . The method of  claim 1 , wherein the unsaturated polyester is prepared by the esterification of at least on ethylenically unsaturated di- or higher polycarboxylic acid or anhydride with saturated or unsaturated di- or higher polyols. 
   
   
       14 . The method of  claim 13 , wherein said polyester is the esterification reaction product obtained by reacting about 5% to about 60% by weight, based upon the total weight of acids, anhydrides and polyols, of unsaturated dibasic acids or anhydrides with a polyol. 
   
   
       15 . The method of  claim 13 , wherein said polyester is the esterification reaction product obtained by reacting about 10% to about 40% by weight, based upon the total weight of acids, anhydrides and polyols, of unsaturated dibasic acids or anhydrides with a polyol. 
   
   
       16 . The method of  claim 15 , wherein the unsaturated acid or anhydride comprises maleic anhydride. 
   
   
       17 . The method of  claim 1 , wherein said polyester is the esterification reaction product of trimethylolpropane, propylene glycol, maleic anhydride, adipic acid, and phthalic anhydride.